Method of making sponge propellant

ABSTRACT

1. A method of forming a shaped, propellant charge having a sponge-like cellular structure which comprises incorporating in a colloided nitrocellulose composition a solvent for an inert gas, placing the said composition in a suitable mold, subjecting said composition to an atmosphere of inert gas at elevated pressures and to heat not exceeding 65*C, and then releasing the gaseous pressure whereby the explosive composition is expanded to form a unitary, spongy structure substantially in the form of the mold.

Ave., Crestwood, Tuckahoe, NY.

Filed: Aug. 27, 1954 Appl. No.: 452,743

Related US. Application Data Division of Ser. No. 352,311, April 30, 1953, which is a continuation-in-part of Ser. No. 57,284, Oct. 29, 1948, abandoned.

US. Cl 264/3 R, 149/2, 149/100 Int. Cl C06b 21/02 Field of Search 18/48 S, DIG. 15, 55 S;

References Cited UNITED STATES PATENTS l/l896 Maxim 102/98 atent 1 91 1111 3,829,537 osenthal Aug. 13, 11974 METHOD OF MAKING SPONGE 2,085,047 6/1937 Schneider 52/201 ux 2,261,630 11/1941 Regestein 52/20 x PROPELLANT 2.372.695 4/1945 Inventor: 1 Henry Rosenthal, I32 Carpenter 2,590,156 3/1956 Carpentier 1. 18/48 Primary ExaminerS. J. Lechert, Jr. Attorney, Agent, or FirmEdward J. Kelly; Herbert Berl EXEMPLARY CLAIM 1. A method of forming a shaped, propellant charge having a sponge-like cellular structure which comprises incorporating in a colloided nitrocellulose composition a solvent for an inert gas, placing the said composition in a suitable mold, subjecting said composition to an atmosphere of inert gas at elevated pressures and to heat not exceeding 65 C, and then releasing the gaseous pressure whereby the explosive composition is expanded to form a unitary, spongy structure substantially in the form of the mold.

3 Claims, 7 Drawing Figures PATENTEDAUB 1 31974 INVENTOR. HEILT'H Ensenihal .ATTDRNE XE;

METHOD OF MAKING SPONGE PROPELLANT This is a division of my copending case Ser. No. 352,311 filed Apr. 30, 1953 which is a continuation-inpart of my application Ser. No. 57,284, filed Oct. 29, 1948, now abandoned.

My invention relates to propelling charges for discharging projectiles from cannon, and more particularly to propelling charges in which the powder is provided with a cellular structure similar to sponge rubber and is formed in such shape as may be required for the particular application. My invention is particularly applicable to propellant charges where obturation is not required and is therefore particularly adaptable for propellant increments for muzzle loading mortars and as the propellant charge for recoilless cannon. However, I do not limit my invention to these uses, as it may also be used in weapons having obturating breech blocks and may be adapted for use in conventional cannon with sliding breech blocks and may further be adapted for use in small arms.

In the art as commonly practiced at the present time, propellant powder is usually principally colloided nitrocellulose (single base) or colloided nitrocellulose and nitroglycerin (double base). In either case the colloid is formed into sheets, tubes, cylinders, strips and similar shapes and dried in these forms. When formed into cylinders, the powder usually has seven holes longitudinal of the cylinder. The speed of burning of the powder is controlled by the composition of the powder, and by the thickness of sheet or in cylindrical powder by the distance between the holes and from the holes to the outside surface of the cylinder (web size). For any particular powder composition, the smaller the web size, the faster is the speed of burning.

In the most commonly used practice, the propellant powder is a dense and substantially solid throughout, except for the longitudinal holes as described above. However, porous powder has been described and used, particularly for use in shotguns. This porous powder, is manufactured by incorporating soluble material such as sugar, barium nitrate, potassium nitrate, or sodium nitrate into the nitrocellulose colloid before drying. The colloid is then formed into grains or flakes, and dried. The soluble material is then leached out of the grains or flakes and the water removed, leaving the grains or flakes porous instead of solid as is the most common practice. The required quantity of these porous grains or flakes is weighed or measured into ordinary cartridge cases under usual conditions.

While I prefer the use of a sponge structure formed by gassing, as will be described later, for use in propelling charges for small weapons with high density of loading, I may use the method of dissolving out soluble material to obtain a porous structure in my propelling charge.

In my invention, I control the speed of buring by the composition of the powder, by density of the sponge, and by the cellular structure of the sponge. Where fast burning powder is required I prefer an open cell sponge; but for charges for larger caliber guns, where a slow burning powder is required, I prefer to use a closed cell structure. The density of the sponge whether open or closed cell may be readily controlled by the amount of gassing provided during the forming operation. Thus the gassing provided for a slow burning powder is less than that which I provide for a fast burning powder. In the former case the sponge will have relatively heavy cell walls and relatively narrow cells, while in the latter case the cell walls are relatively thin and the cells are relatively large. This has the same effect on the powder that is achieved by changing web size on conventional tubular powder.

In the production of my cellular propellant, I mold the propellant into the shape required for the particular application. Thus for recoilless cannon, I mold the propellant into the shape of the cannon chamber and provide a core in the mold which forms a chamber for the black powder ignition charge. Also in this application I may mold threads or other means into which a percussion cap or other initiating charge may be adapted. Thus in this application, my propelling charge requires no cartridge case, primer tube or other large metallic member as is used in the present art and the whole is consumed except for minor portions of the charge as are used in the assembly of the initiating means. These parts are so small that they will be blown out of the weapon even when multiple venturi tubes are used to obtain the recoilless action. Moreover, substantially the entire weight of the charge is useful in propelling the projectile, which desirable property is not achieved when conventional propellant is used in a cartridge case, either of metal or of frangible material.

For mortar increments, I mold my propelling charge into the shape desired for the particular ammunition, preferably in the shape of a flat doughnut to fit over the boom of the mortar projectile fin or over the rear end of the projectile. Such a doughnut may be slitted so that it may readily be placed on or removed from the round.

One advantage of my slitted doughnut type increment over the present conventional mortar increment lies in the advantageous properties from which the charge is made. Thus it is possible to impart any desired degree of resilience to mortar increments molded from a given batch of the sponge-like material made by my process, by controlling the chemistry of the composition before molding, a high degree of resilience being desirable for mortar increments because they require manipulation in loading. Another advantage of such an increment over the present conventional mortar increment lies in the fact that my increment may readily be made waterproof as will be described later.

For charges for weapons with obturating breech block, I mold my propellant into a shape having substantially the same form as the finished conventional wrapped charge as is now commonly used. Where the weight of the charge is such that it is desirable to use a sectional charge, I may provide means of interlocking the sections as they are inserted into the weapon. This is particularly advantageous where the sections are provided with longitudinal cores for a black powder primer charge. It also may be used for withdrawing the charge from the weapon, if the weapon is charged and not fired. My propelling charge in this instance completely eliminates the use of cartridge cloth bags which are not only expensive to make and load, and the materials of which are difficult to obtain, but also may lead to dangerous embers being left in the gun from unconsumed portions of the fabric.

When used as propelling charge for weapons with a sliding breech block, my propelling charge may be molded with a stub cartridge case which acts as the obturating means. In this manner, considerable strategic metal may be saved besides greatly reducing the weight of the round.

For whatever purpose my propelling charge is used, it may be readily made waterproof in a simple manner. Thus it may be sprayed with a waterproofing film, or dipped in a waterproofing solution after the sponge is removed from the mold. I prefer the latter method, in which I dip the formed sponge in a solution of ethyl cellulose, polyvinal chloride, polyethylene, cellulose acetatebutyrate, or similar material. On removing the molded piece from the solution, draining, and eliminating solvent, there is formed a thin coating around the molded pieces which adheres to the propelling charge and forms a continuous water vapor barrier entirely surrounding the molded sponge of propelling powder.

As the propelling charge is thus made substantially waterproof, packing for the round in which my invention is used may be designed primarily for mechanical protection, rather than for both mechanical protection and as a water vapor barrier. This water resistance is of particular benefit in mortar rounds, where the ammunition is frequently prepared for firing and left without protection against moisture at the mortar position.

It may be that with propellant material of certain formulae, the waterproofing film may not be compatible with the material of the propellant, that the waterproofing film and a component of the propellant may be mutually soluble or it may for other reasons be desirable to provide the waterproofing coat over a coating that does not have the required properties as a water vapor barrier. In such event, I provide a laminated coating on the propellant charge. Thus, I first provide a coating by spraying or dipping using a material that is compatible both with the powder and with thematerial used as a waterproofing coating. Such a coating for chemical inertness with the propellant material would not in itself necessarily be a water vapor barrier. After this chemically inert coating has dried sufficiently, I place on the outside the waterproofing coating previously described. One form of laminated coating that I have found to be suitable is an initial coating of polyvinal alcohol produced by dipping my propellant in a solution of this material. When this coating had dried a coating of cellulose acetate-butyrate is applied by dipping in a suitable solution of this material as for instance, a solution of cellulose acetate-butyrate in chloroform.

With certain propellant compositions it may be necessary to use a triple laminated coating, in which the outer layer is the waterproofing lamination, the inner layer is compatible with the propellant material, and the center layer is of material mutually compatible with the inner and outer lamination.

ln gassing the propellant to form the sponge, I prefer to first press the propellant roughly into approximately the form desired before placing it into the molds for gassing. With single base nitrocellulose powder, this pressing step is preferably undertaken on a weighed amount of colloid from a step in the powder process where the colloid has the required solvent control. The weight used should make allowance for elimination of solvent in the final sponge. [t is necessary that a certain amount of solvent be left in the colloid before gassing in order to maintain the plasticity of the colloid during the gassing operation. The residual solvent also acts as a gassing agent and to dissolve other gassing agents such as carbon dioxide gas, ammonia, nitrogen or other gases. Also in some instances it may be desirable to add a blowing agent to the smokeless powder during the colloiding stage. Such an agent added to the colloid may be a low boiling liquid or solid such as dimethylamine which depends for its blowing action upon its vaporization, or it may be suitable solid or liquid which decomposes into gases at low temperatures. Suitable inorganic compounds may be used for this purpose. Where gaseous agents are used they may be applied under pressure up to 15 atmospheres.

The amount of solvent left in the colloid before subjecting the colloid to the blowing action must be regulated in accordance with the character desired for the final sponge propellant. This is due to the fact that the viscosity of the colloid will be in considerable part controlled by the solvent content. Where open cell sponge is desired the colloid, before blowing, should be less viscous than when closed cell sponge is desired. The amount of solvent to provide the required viscosity will depend on the particular propellant composition. Generally compositions with appreciable amounts of plasticizer will require less solvent to provide the proper viscosity than compositions having a small amount of plasticizer. Where an open cell sponge with a high volume of voids is desired (such as for use where a fast burning rate is required) more solvent may be left in the colloid before gassing than where a closed cell sponge with a low volume of voids is desired (such as for use where a slow burning rate is required). During the gassing operation substantially all of the solvent will be elimated from the colloid, particularly where an open cell sponge with a high volume of voids is required for the particular use.

Where double base powder (nitrocellulose, nitroglycerin) is required, the normal colloiding operations use the nitroglycerin for producing the colloid with the nitrocellulose and sometimes no other solvent is required in the process as now conducted. However, when making a cellular or sponge double base powder it may be desirable to add an amount of low boiling solvent such as ether to assist in the gassing operation. Also other liquid or solid gassing agents may be added during the colloiding step as described above in connection with their use in the manufacture of sponge single base powder.

With either single or double base powder the addition of alkyl acetates as a component of the solvent greatly adds to the plasticity of the colloid and is of material assistance in the later gassing operations. Thus in my sponge propellant process, I prefer to add some alkyl acetate to the colloid preparatory to the gassing operation. Any of the lower carbon alkyl acetates are suitable for this purpose, however, I prefer the use of methyl acetate, ethyl acetate, or iso-propyl acetate to either propyl acetate or amyl acetate on account of the lower boiling temperature of the former group and consequently the greater ease of their elimination during the gassing step of my process.

It will be difficult in my process to produce a sponge propellant charge in which the entire charge corresponds to a charge having a single web thickness of granular, cord, strip, or sheet propellant. The sponge will have some variations throughout its mass both as to size of voids and thickness of cell wall. However, if the process is properly controlled, close uniformity in effective cell size and wall thickness can be secured so that each charge has substantially the same burning rate as other charges of the same design. Such a charge would have in general the same burning characteristics as is now obtained with a dual granulation charge.

Not only do I control the cell size of the sponge and composition of the propellant to provide the proper burning rate, but I also control other physical properties of the charge to provide the proper structure for the particular application. This is accomplished by control of the chemistry of the charge and particularly by the amount of plasticizer incorporated in the colloid. Thus for use in recoilless weapons, I prefer a hard nonpliable structure that will be assembled into a rigid complete round for service into the weapon. On the other hand, I prefer that mortar increments be pliable and relatively soft and their inherent resiliency enables them to be readily placed around, or removed from the boom of a mortar projectile, as the range observations may dictate at the time of firing.

The advantages of my invention are thus:

1. It reduces the weight of the ammunition.

2. It completely eliminates the necessity for cartridge cases for recoilless weapons.

3. It provides a propelling charge that is easily and cheaply made waterproof.

4. It eliminates the necessity for cartridge cloth on charges for large caliber weapons with obturating breech blocks.

5. It provides ready means for controlling the speed of burning of the propelling charge.

6. It provides a propelling charge that can be packed in simplified packing.

7. It reduces the amount of drying with single base propellant.

Other advantages of my invention are evident from this specification.

My invention may be more readily understood from the following description and examples taken together with the drawings which form a part of this specification, and in which FIG. 1 shows my invention applied to a charge for a recoilless cannon.

FIG. 2 shows a transverse sectional view of my invention applied to a mortar increment along line 22 of FIG. 3.

FIG. 3 shows a longitudinal view along line 3-3 of FIG. 2.

FIG. 4 shows my invention applied to sectional propelling charge for a large caliber weapon with obturating breech block.

FIG. 5 shows my invention applied to a propelling charge for a conventional weapon with sliding breech block.

FIG. 6 shows a transverse sectional view of the mor tar increments of FIGS. 2 and 3 after attachement to the boom of a mortar projectile.

FIG. 7 shows a transverse sectional view of mortar increments similar to those shown in FIGS. 2 and 3, but adapted to be used on a projectile boom of frustoconical form.

Referring to FIG. 1, the propelling charge 1 is formed to the shape of the gun chamber for which it is designed. The sponge propellant 2 is provided with the cored central tube 3, which is adapted to be loaded with the black powder ignition charge 4. The tube 3 is shown to be closed by the frangible plug 5 containing the igniter cap 6 and the striker 7. The conical frustrum 8 is shown as formed to fit the boat-tail of a projectile. If the projectile does not have a boat-tail the shape of the front end of the charge may be modified to suit. The drilled out portion 9 provides means for adjusting the weight of the charge where such adjustment may be found necessary. After the charge weight is adjusted, the necessary ignition powder is placed in the cylindrical core and the core closed with the frangible plug with cap and striker, the assembly is sprayed with or dipped in a suitable liquid such to form a layer completely surrounding the propellant charge as has been more fully described. This layer, after drying, is preferably from .003 to .007 inch thick and forms a moisture vapor barrier completely surrounding the charge. The projectile may then be inserted in the conical frustrum 8 and may be attached thereto with any suitable cement to make a fixed round of ammunition.

As an example of the method of producing such a propelling charge for a recoilless cannon, I make a mold having the shape shown in FIG. 1, including the cavity for the ignition charge, but not including the hole 9, which is drilled, if required, after the charge is completed, for the purpose of adjusting the charge weight. In the example the total volume of the mold, which is substantially the volume of the finished charge, it taken as 200 cubic inches.

I place in the mold an amount of 5.1 pounds of nitrocellulose colloid having the following composition:

Nitrocellulose (13.25%N) 98 parts Diphenylamine 1 part Potassium Sulphate l part Ethyl Alcohol 25 parts Di-ethyl Ether 45 parts Total I parts I place one or more molds, each with the required amount of nitrocellulose colloid, in an autoclave and add carbon dioxide until a pressure of approximately seven atmospheres is established. I then apply heat to a temperature of 65C. After this temperature has been established, I release the pressure from within the autoclave. This reduction in pressure permits the carbon dioxide and part of the solvent vapors to be expelled from the mass of nitrocellulose colloid expanding the colloid to fill the mold as a sponge structure. I may then apply a vacuum to remove further portions of the solvent. The formed sponge charge is then removed from the mold and the remaining volatile solvent may be eliminated from the charge by placing the charge in a current of air heated to about 50C.

In order to improve the plasticity of the colloid and assist in absorption of the gassing agent, I may add an alkyl acetate to the nitrocellulose colloid. As an example (using the same 200 cubic inch charge) I place in the mold an amount of 5.9 pounds of nitrocellulose colloid having the following composition:

Nitrocellulose (13.25%N) 98 parts Diphenylamine 1 part Potassium Sulphate l part Ethyl Alcohol 25 parts Di-ethyl Ether 45 parts Ethyl Acetate gs parts Total I parts The process is carried on as described in the example above, except that a lower pressure of carbon dioxide is required for the gassing due to the greater absorptive capacity of the colloid resulting from the addition of the alkyl acetate.

In each of the examples above, there is formed a shaped propelling charge, ready for the primer, igniter, and waterproofing.

Referring to the modification illustrated in FIGS. 2, 3, 6 and 7, which show split toroidal, cylindrical or doughnut-shaped increments 11 (FIG. 6) and 11 (FIG. 7) intended to fit over the boom of fin stabilized projectiles 32 for use with smooth bore mortars. The increments 11 and 11 are shaped from integrally molded explosive material having expanded, spongelike cellular structure madetfrom suitable composition according to my method. FIG. 3 is taken on the line 3-3 of FIG. 2, through the slit 31 which is cut through the annulus and may be radial as shown or in planes offset with respect to the central axis of the increment. This slit makes possible easy assembly and manipulation of the resilient increments incidental to placing them on or removing them from the boom of the mortar projectile. Generally it is not known until the range is determined just before firing how many increments will be required to give the projectile the necessary muzzle velocity for that range. FIG. 7 shows a projectile having a frusto-conical boom of forwardly increasing diameter. In changing such a boom, increments of corresponding diameters must be used, each having identical volumes of explosive material, the increase in internal diameter in the forward direction being compensated by a corresponding increase in axial dimension of the respective increments so that all have the same mass of propellant. If, after the charge is assembled, it becomes necessary to remove one or more of the increments immediately before firing, this can readily be accomplished by a simple manipulative movement, because of slit 31 and the inherent resiliency of the material of which the increment is composed.

As an example of the method of producing such a mortar increment, I make a mold having the shape shown in FIG. 2, in which the outside diameter of the annulus is 3 inches, the inside diameter is 1% inches, and the thickness of the annulus is /2 inch.

1 place in the mold 250 grains of colloid having the following composition:

Nitrocellulose (13.25%N) 52.25 parts Nitroglycerin 4300 parts Diethyphthalate 300 parts Potassium Nitrate 120 parts Ethyl Centralite 060 parts Acetone 25.00 parts Total 125.00 parts I place one or more molds, each with the required amount of colloid, in an autoclave and add carbon dioxide until a pressure of approximately ten atmospheres is established. I then apply heat to a temperature of 50C. After this temperature has been established, I release the pressure from within the autoclave. This reduction in pressure permits the carbon dioxide and part of the solvent vapors to be expelled from the mass of the colloid, expending the colloid to fill the mold as a sponge structure. I may then apply a vacuum to remove further portions of the solvent. The formed sponge increment is then removed from the mold and the remaining volatile solvent may be eliminated by placing the increment in a current of air heated to about 50C.

As with the example of a recoilless charge as has been described, I may add an alkyl acetate to the colloid when making mortar increments. As an example, I place 300 grains of colloid of the following composition in the mold described above:

Nitrocellulose (13.25%) 52.15 parts Nitroglycerin 43.00 parts Diethythphthalatc 3.00 parts Potassium Nitrate 1.25 parts Ethyl Centralite 0.60 parts Acetone 25.00 parts Methyl acetate 25.00 parts The process is carried on as described in the example above, except that a lower pressure of carbon dioxide is required for the gassing due to the greater absorptive capacity of the colloid resulting from the addition of the alkyl acetate.

In each of the examples above, there is formed a shaped mortar increment, ready for weight adjustment and waterproofing.

Referring to FIG. 4, the charge shown is a composite charge consisting of a base charge 13 and two increment charges 14 and 15. Each of these sections is separately molded to the desired shape with central core 3 adapted to receive a black powder ignition charge 4. The base section 13 and the increment 15 are also molded with pockets 16 and 17 respectively also to receive black powder charges 18 and 19 respectively. A small depression 20, is also provided at the front end of the base charge, the rear end of the forward increment, and at both ends of the intermediate increment. A bayonet lock joint 21 may be molded at the juncture of adjacent sections to make compact interlocked unit when the charge is placed in the gun chamber. This construction will also be of assistance in removing the charge from the chamber when it is desired to do so. After the base section is molded as described above and the charge weight adjusted in any suitable manner, a thin disc of metal foil or other suitable material is placed in the pocket 20, the black powder charges 4 and 18 are placed in position and the pocket 18 is closed with a suitable closure member such as the frangible disc 22. The base charge 13 is now ready for waterproofing with the continuous layer 10 of water-resisting material such as has been described in connection with FIG. 1. The forward increment 15 is constructed in a manner similar to that described for the base increment. As shown the intermediated increment has no igniter pad. Otherwise, it is constructed in a manner similar to that described for the base and forward increments.

Referring to FIG. 5, the charge 24 is molded of sponge propellant 2, with the stub cartridge case 25 of brass or other suitable material used as an insert in the mold in which the sponge is formed. In this instance the moisture resistive layer 10, is not required to completely surround the propelling charge, but may stop on the stub cartridge case and be bonded thereto. After the charge has been waterproofed as described previously, the black powder charge 4 may be inserted in the cored portion of the charge 3, and the primer 26 may be applied to the stub cartridge case 25.

In the following claims, the term propellant charge is intended to mean a unified structure of propellant explosive, formed in the required shape to fit a gun chamber, or to form an increment as described. It is not intended to define a porous propelling powder formed into small grains, flakes, or other forms, a multiplicity of which are inserted into a cartridge case to make the propelling charge.

I claim:

1. A method of forming a shaped, propellant charge having a sponge-like cellular structure which comprises incorporating in a colloided nitrocellulose composition a solvent for an inert gas, placing the said composition in a suitable mold, subjecting said composition to an atmosphere of inert gas at elevated pressures and to heat not exceeding 65C, and then releasing the gaseous pressure whereby the explosive composition is expanded to form a unitary, spongy structure substantially in the form of the mold.

acetate is ethyl acetate. 

1. A METHOD OF FORMING A SHAPED. PROPELLANT CHARGE HAVING A SPONGE-LIKE CELLULAR STRUCTURE WHICH COMPRISES INCORPORATING IN A COLLOIDED NITROCELLULOSE COMPOSITION A SOLVENT FOR AN INERT GS, PLACING THE SAID COMPOSITION IN A SUITABLE MOLD, SUBJECTING SAID COMPOSITION TO AN ATMOSPHERE OF INERT GAS AT ELEVATEF PRESSURES AND TO HEAT NOT EXCEEDING 60*C, AND THEN RELEASING THE GASEOUS PRESSURE WHEREBY THE EXPLOSIVE COMPOSITION IS EXPANDED TO FORM A UNITARY, SPONGY STRUCTURE SUBSTANTIALLY IN THE FORM OF THE MOLD.
 2. A method of forming a shaped, propellant charge which comprises incorporating in a colloided nitrocellulose composition an alkyl acetate as a solvent for a gas which is inert to said composition, placing the said composition in a suitable mold, subjecting said composition to an atmosphere of inert gas at elevated pressures and to heat not exceeding 65*C, and then releasing the gaseous pressure whereby the explosive composition is expanded to form a unitary, spongy structure substantially in the form of the mold.
 3. The method recited in claim 2 wherein said alkyl acetate is ethyl acetate. 